I 100% agree that Hipmunk is an easy, great service. Just keep in mind that Southwest airline (last time I checked) does not play nice with HM. So if SW is your preferred carrier, make sure to check them independently.

I’ve been studying abroad for a year in the UK. I booked my overseas flights with Hipmunk and it’s fantastic, but there is a small caveat: Hipmunk doesn’t aggregate European budget airlines, so once you’re in Europe, you’ll have to do your own legwork on Easyjet, RyanAir, FlyBe, or Flavor-Of-The-MonthAir flights. I recommend trying Skyscanner for anything like that.